Chromosomal and chromatid aberrations

The disadvantages of cytogenetic assays are that they are time-consuming and that negative results indicate only that further studies must be conducted with S-9 activation and with multiple fixations to account for possible different sensitivities of stages of the cell cycle. Furthermore, the scoring of 300 cells per point for chromosomal and chromatid aberrations is very difficult, requires much expertise, and is necessary to establish an accurate result. 

Chromosomal aberrations include both numerical and structural aberrations. Numerical aberrations are changes in the number of chromosomes of the normal number characteristic of the animals utilized (aneugenicity). Structural aberrations are classified into two types, chromosome or chromatid aberrations (clastogenicity). Chromosomal mutations and related events are the cause of many human genetic diseases and there is evidence that chromosomal mutations and related events are involved in cancer development. 

This in vitro cytogenetic test is a clastogenicity test system for the detection of chromosomal aberrations in cultured mammalian cells or primary cultures. Chromosomal aberrations may be either structural or numerical. However, because cytogenetic assays are usually designed to analyze cells at their first posttreatment mitosis and numerical aberrations require at least one cell division to be visualized, this type of aberration is generally not observed in a routine cytogenetic assay. The best estimate of aberration frequency is the first cell division after the start of treatment. Structural aberrations are of two types chromosome or chromatid aberrations. 

The nucleus of all eucariotic cells contains the carrier of the genetic information in the chromosomes. It is possible to visualize the chromosomes and analyze their number and pattern during a special period of cell division (the metaphase). Alterations from their normal shapes are observed as structural chromosome aberrations. These are chromosome type aberrations (terminal and interstitial deletions, dicentrics and rings), chromatid aberrations (gaps, breaks and exchanges) and sister chromatid exchanges. Spontanous frequencies of such chromosome... 

The classification and nomenclature of the International System for Human Cytogenetic Nomenclature (ISCN, 1985) as applied to acquired chromosome aberrations is recommended. Score sheets giving the slide code, microscope scorer s name, date, cell number, number of chromosomes and aberration types should be used. These should include chromatid and chromosome gaps, deletions, exchanges and others. A space for the vernier reading for comments and a diagram of the aberration should be available. 

Stmctural chromosome aberrations may be of two types, chromosome or chromatid. A chromo-some-type aberration is a stmctural chromosome damage expressed as breakage, or breakage and... 

In genotoxic assays inorganic arsenicals are either inactive or weak mutagens but are able to produce chromosomal effects including aberrations and sister chromatid exchange in most test systems. Studies of exposed human have detected higher incidences of chromosomal aberrations in peripheral lymphocytes and increases in the frequency of micronuclei in the oral mucosa cells, urothelial cells, and peripheral blood lymphocytes. ... 

Occupational exposure of 20 workers to pentachlorophenol at concentrations that ranged from 1.2 to ISOpg /m for 3-34 years did not result in any increased incidence of sister chromatid exchanges or chromosomal aberrations. In another report, significant increases in the incidence of dicentric chromosomes and acentric fragments were detected in the peripheral lymphocytes of exposed workers the frequency of sister chromatid exchanges was not increased." ... 

Aberrations in chromosomes or chromatids, which are sometimes microscopically visible, may arise during mitotic division when newly divided chromosomes fail to separate or do so incorrectly. The absence of a chromosome is usually lethal, and an excess is often poorly tolerated, giving rise to serious defects. Aberrations of the sex chromosomes are more readily tolerated, however. Chromosome aberrations may be caused by foreign compounds as indicated in the section on mutagenesis (see chap. 6). However, those cells with aberrations seem to be rapidly eliminated and so may contribute to cell death rather than a heritable mutation. 

Chromosome aberrations have been reported in Syrian hamster embryo (SHE) cells after treatment with a DMSO extract of tryptophan pyrolysate. At a dose of 30 pg/ml, 69 exchanges and 29 chromosome or chromatid breaks were observed among 200 metaphases. Gaps and minutes were noted as well (33). Sasaki, et al. (34) also observed chromosome aberrations in human and Chinese hamster cell lines after exposure to Trp-P-1 and Trp-P-2. 

A simpler, quicker, and less expensive cytogenetic test uses sister chromatid exchange (SCE). SCEs are detected in chromosomes that have been treated in such a way that the two sister chromatids of a chromosome differ chemically and thus stain differently. Most chemical mutagens induce SCEs at concentrations lower by a factor of about 100 than those needed to produce significant yields of ordinary chromosomal aberrations. The major exception to this is the small group of chemicals that, like x rays, produce double strand breaks in DNA and induce aberrations at all stages of the cell cycle. 

Lack of chromosomal aberrations has been shown for CPs studied in mammalian cells collected from animal experiments (reviewed in [6]). Sexually mature male Fischer-344 rats administered the SCCP Cio-12 58% Cl by gavage once daily for 5 days at concentrations up to 750 mg/kg/bw/day, did not show an increased mortality or frequency of chromosome or chromatid abnormalities in bone marrow cells [27]. Similarly, no chromosomal aberrations were found for an MCCP (Ci4 i7 52% Cl) in the same experimental design at doses up to 5,000 mg/kg/day [28] or in two LCCP formulations (one with 70% chlorination, the other C22-26, 43% Cl) at doses up to 5,000 mg/kg/day [29, 30]. MRl mice given single doses of 50 and... 

Acetaldehyde produced chromosomal aberrations including chromosomal fragments, achromatic lesions and chromatid breaks in metaphases at 12 hr and 24 hr in primary cultures of rat skin fibroblasts. Dose-related increases in aneuploidy were also observed... 

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